Throughout the fiberline, i.e. the different process steps involved when converting wood chips or other fibrous raw material into pulp, there are several positions where mixing apparatuses are used to mix different kind of media into the pulp suspension. The treatment media added into the fiber suspension may for example be for heating, delignification or bleaching purposes. The treatment media may be in liquid or gaseous state.
When mixing treatment media into a fiber suspension, the issue of even and homogeneous distribution is of high importance for the mixing result achieved. A well-known mixer type is disclosed in international application WO2004/052517. The mixing device described in WO2004/052517 comprises a housing with a wall defining a mixing chamber into which pulp suspension is fed by a first feeder. The device further comprises a rotor shaft with a rotor body, arranged to produce turbulence in a turbulent flow zone. A second feeder is arranged to distribute a chemical medium into or in close vicinity to the turbulent flow zone.
Although the mixing efficiency is good in the mixer disclosed above, there is still a need for an improved device with a further enhanced mixing efficiency. As the production capacity for a fiberline increases, the flow rate through the mixing apparatuses in such fiberlines increases, which leads to shorter residence times in the mixing chamber.
Accordingly, there is a need for an improved mixing unit and a mixing apparatus